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United States Patent Office 3,647,579 ?atenterii July 3i, 19(82 ti, efficiently effects the oxidation of the N-oxides of all of 3, 47,579 PRGQW‘ ' the tertiary amines which are known to oxidize to the corresponding N-oxides, and in fact my new process is PREEJARPIG N-OXEBIES Robert ‘S. Witman, ‘Wsst‘iield, NJ, assignor to Sheil Gil applicable generally to the oxidation of all tertiary amines (Iornpany, a corporation of Delaware No Drawing. i i Filed .liuly 18, 1958, §er. No. ‘749,345 to the corresponding N-oxides. Since my new process employs only stable, easily handled materials, relatively inexpensive, re-usable catalysts, and gives much higher This invention pertains to a process for the preparation of N-oxides—that is, amine oxides. reaction rates than have heretofore been possible, it lends itself admirably as a general method for the large-scale More particularly, this invention provides a novel, improved process for the preparation of N-oxides. The new process also effects preparation of N-oxides of tertiary organic bases-Le, 10 much more efficient use of hydrogen peroxide. tertiary amines. Any tertiary amine in which the amino nitrogen atom The N-oxides are a class of compounds of which vari ous members have been found to have properties which make them useful for a Wide variety of purposes. Thus, is the primary reactive moiety is oxidized to the corre sponding N-oxide by my new process. Suitable amines thus include the tertiary amines in which the groups di the halo-pyridine N-oxides have been found to be effec rectly bonded to the amino nitrogen atom are hydro tive fungicides, as have the N-oxides of the nitrogenous carbon groups, and those in which the groups directly condensation products of methylol-forming phenolic com bonded to the amino nitrogen atom are substituted-hydro pounds, formaldehyde and aliphatic secondary amines. carbon in character. The groups bonded to the amino These latter N-oxides also have been found to be of value 20 nitrogen atom may be aliphatic or ‘aromatic in character. as moth-proo?ng agents, and as bactericides, as ?nishing The aliphatic groups may be of branched-chain or of agents for textiles, as water-proo?ng agents for textiles, and for rendering textiles more receptive to dyes. Also, the N-oxides of heterocyclic bases, such as the phenan straight—chain con?guration, or they may be cyclic in character; they may be saturated, or they may be ole?ni throlines, quinoxalines, quinolines, isoquinolines and py ridines, have been found to have valuable therapeutic properties and low mammalian toxicity. N-oxides also groups preferably are excluded, since the acetylenic link tivity of the amino nitrogen atom. The amino nitrogen have been found to be useful as stabilizers for unsatu atom may form a part of a heterocyclic ring, and in such cally unsaturated. Actylenically unsaturated aliphatic age in some cases may interfere with the necessary reac rated compounds such as styrene, and as wetting agents, Washing agents, cleaning agents, emulsifying agents, and for other uses which involve modi?cation of the surface properties of aqueous media. Many of the N -oxides also cases, the remaining atoms of the ring may be only carbon 03 C; atoms, or they may be such atoms as the oxygen atom, the sulfur atom, metal atoms or semi-metal atoms. The suitable tertiary amines may be homogeneous in char acter-—all of the groups bonded to the amino nitrogen ring being similar in character—or they may be hetero, are of interest as raw materials for the preparation of other valuable compounds. It has been proposed that the N-oxides be prepared by reacting a tertiary amine with perbenzoic acid, peroxy geneous in character—i.e., mixed amines wherein two or more of the groups bonded to the amino nitrogen atom acetic acid or like organic per-acids, in an organic solvent. However, such organic per-acids are highly unstable, so I are dissimilar in character. Suitable amines thus include those wherein the groups bonded to the amino nitrogen atom are alkyl, aryl, that they must be prepared freshly just before use, and great caution must be exercised in their use to prevent 40 their detonation. Further, these organic per-acids are expensive to prepare and use. Consequently, processes involving the use of such acids are not feasible for the large-scale preparation of ‘til-oxides. Examples of the suitable types of tertiary amines in clude the trialkyl amines such as trimethyl, tributyl, tri It also has been proposed that the N-oxides be pre pared by reacting a tertiary amine with hydrogen perox~ ide in an aqueous reaction medium. octyl, methyl diethyl, isopropyl diamyl, pentyl' methyl This method like butyl and like amines, alkyloi amines such as triethanola wise is not feasible for the large-scale production of N mine, triisopropanolamine, and the like, mixed alkyl alkyloi amines, such as diethyl ethanolamine, aryl oxides because the reaction times involved are much too long. To overcome the shortcomings of such processes, it has been proposed that the reaction of a tertiary amine with hydrogen peroxide be carried out in the presence of particular reaction media, particularly oxygen-containing organic liquids such as lower carboxylic acids (glacial acetic acid in particular) and lower ketones (acetone in particular) . These latter proposals have not provided any satisfac tory method for preparing N-oxides, inasmuch as the elfectiveness of the use of particular solvents in e?ecting the oxidation of the amine to the N-oxide varies greatly from case to case. Thus, in some cases, the use of an oxygen-containing organic solvent results in e?icient oxi dation of the amine, while in other cases such a solvent is Wholly ineffective in promoting the oxidation of the amine. I have now discovered that tertiary amines, as a class, are easily and e?‘iciently oxidized to the corresponding N-oxides by reacting those amines with hydrogen perox aralkyl, alkaryl, alkenyl, alkenyl-aryl, aralkenyl groups i.e., hydrocarbon groups—or alkylol, haloalkyl, haloaryl, hydroxyaryl, haloalkaryl, haloaralkyl, haloalkenyl or ‘like substituted-hydrocarbon groups. 50 amines such as triohenylamine, mixed alkyl ‘aryl amines such as dimethyl aniline, araikyl amines such as tribenzylamine, alkaryl amines such as tri-p-tolyl amine, mixed, allyl diethylamine, phenyl ethyl allylamine and the like, halogen~substituted hydrocarbon amines such as tris(beta-chloroethyl)amine, beta-chloroethyl di methylamine, tribromomethyl diethylamine, phenyl beta, 'beta-dichloroethylamine, tris(p-chlorophenyl)amine, p bromophenyl dihexylamine, ‘and the homologs and ana logs of such amines. Suitable amines of interest because of the properties of the corresponding N-oxides are the trialkylamines containing up to 35 carbon atoms, and particularly such amines wherein one of the alkyl groups is a long-chain alkyl group of from 8 to 20 carbon atoms (such as the capryl, lauryl, cetyl, stearyl or octadecenyl groups) and the other two alkyl groups are lower alkyl groups of up to 6 carbon atoms each, or those other two alkyl groups form a single alkylene group, as in the piperidine or pyrrolidine rings. Suitable amines also of interest ‘because of their amine oxides are the tertiary ide in the presence of unstable inorganic per-compounds 70 amines of the formula (R) (R') (R”)N, wherein R is a of acid—forming elements of groups VA, VIA, VIE and hydroaromatic moiety, or wherein R is an alkyl group VIII of the periodic table, as catalyst. My new process of up to 20 carbon atoms bonded to the nitrogen atom 3,047,579 3 by an oxyalkylene (—-O-alkylene-) group, by an amido alkylindolcs, N-alkyl pseudoindoles, N-alkyl isoindoles and pseudoisoindoles, 4-quinolizine, the N-alkyl 2~benz alkylene (—-C(O)NH-alkylene-) group, or by an aro azocines, the N-alkyl 7,8~benzoheptamethylenimines, the matic nucleus such as the phenyl nucleus. Still another N-alkyl cyclopenta(b) -pyrroles, and the corresponding group of N~oxides of interest are those derived from U! (c)-pyrrol_es, the N-alkyl nortropanes, the N-alkyl 1,4 amines of the structurev and 1,6-pyrro1opyridines and S-pyrindoles, the N-alkyl aliphatic oxazolo(5.4-b)pyridines, the various isomeric diazacyclo long-chain cycloalkyls, such as 1,15-diazacyclotriacon tane, the various isomeric tetrazocyclo-long-chain cyclo aliphatic wherein R is an aromatic or substituted-aromatic nucleus, 10 alkyls, such as 1,4,8,ll-tetrazotetradecane, the N-alkyl-l azapiro(2.4)heptanes, (2.5)octanes and the like, conidine, this class of compounds being condensation products of and other similar tertiary heterocyclic amines. According to the process of this invention, the tertiary amine is oxidized to the corresponding N-oxide by react Patents Nos. ‘2,031,557, 2,033,092, 2,036,916, 2,045,517 ing the amine with hydrogen peroxide in the presence of a and 2,220,835. The precise nature of such amines and 15 catalyst consisting of an unstable inorganic per-compound detailed descriptions thereof is set out in the last-men of an acid-forming element of groups VA, VIA, VIB and tioned of this series of patents. VIII of the periodic table. These catalysts are provided A particularly wide variety of properties are exhibited by the oxides and/or acids of the speci?ed elements and by the N-oxides of heterocyclic bases wherein the amino nitrogen atom is one member of the heterocyclic ring, 20 acid salts of those acids, which oxides, acids or acid salts form inorganic peracids or acid salts of inorganic per any valence bond of the trivalent nitrogen atom not in acids (persalts) in the reaction zone. Although the actual volved in the ring being satis?ed by a hydrocarbon group, catalysts are the per-compounds of the acid-forming ele or a halo- or hydroxy-substituted hydrocarbon group as methylol-forming phenolic compounds, formaldehyde and aliphatic secondary amines described in United States set out hereinbefore. Preferably, the amines from which ments of groups VA, VI and VIII, these catalysts are 35 carbon atoms, the heterocyclic moiety containing not oxides, acids or acid salts of those elements. Herein, for brevity, the source oxides, acids or acid salts also will such N-oxides are prepared contain not more than about 25 actually formed in situ in the reaction zone from the more than about 20 carbon atoms. Heterocyclic amines be termed “catalysts.” Any of the oxides, acids and acid salts of the acid-forming elements of groups VA, VI and VIII of the periodic table which are known to be effective wherein the heterocyclic ring involves only nitrogen, carbon, oxygen and sulfur atoms, and any substituent group or groups is(are) hydrocarbon, preferably lower in promoting hydroxylation of ethylenic compounds by alkyl or phenyl, halogen or hydroxyl are preferred. hydrogen peroxide are suitable as catalysts in the present These amines suitably may contain but one, or they may Thus, acids, salts of acids, or oxides which re . PI‘OCCSS. contain two or more amino nitrogen atoms, and may con act readily with hydrogen peroxide to form peracids can tain one, or they may contain two or more hetero rings, one or more than one amine nitrogen atom being present 35 be used. Oxides and acids of the acid-forming elements in each ring. Typical of such heterocyclic N-oxides are those derived from such heterocyclic amines as pyridine and the various of group VI of the periodic tableare a particularly useful class of catalysts. These oxides may be used as such, substituted pyridines, such as the alkyl-substituted pyri dines, including both the N~substituted hydropyridines (dihydro-, tetrohydro- and hexahydropyridines), and the C-substituted pyridines such as the picolines, lutidines, collidines and parvolines, phenylpyridine, pyridyl-pyri dines, halo-substituted pyridines, such as chloropyridine, dibromopyridine, ‘and the like, quinoline and its substitu tion products, isoquinoline, hydroxyquinoline, and the various hydroquinolines and their substitution products, phenanthrolines and their substitution products, the quin oxalines, and other pyrazines, such as pyrimidine, pyra may be convertedto the salts, preferably acid salts, or 40 partial salts, thereof particularly the alkali metal or am monium salts thereof. Alkaline earth metal and other salts of these acids likewise may be used, though they are as may the acids themselves be used, or the acids or oxides somewhat less eifective in some cases. aration are set out in detail in United States Patents Nos. 2,754,325 and 2,773,909. For the purpose of brevity without sacri?ce of detail, the portions of U.S. 2,754,325 and U.S. 2,773,909 describing the heteropoly acids of-the acid forming elements of group VI of the periodic table zine and the like. Speci?c examples of other suitable ter tiary amines in the preparation of N-oxides by the proc ess of this invention include 2-azirine, N-substituted 2 aziridines, 1,3-diazete, uretine, N-alkyl uretines, l-alkyl-, 3-alkyl-, and 1,3-dialkyl-1,2-diazetidines, N- and N,N' substituted piperazines, azete, N-alkyl azetines, N-alkyl acetidines, oxazole, N-alkyl oxazolines, N-alkyl oxa'zoli dines, l-alkyl-imidazoles, 1-alkyl-, 3.-alkyl- and 1,3-dialkyl dines, l-alkyl-imidazoles, l-alkyl-, 3-alkyl- and 1,3-dialkyl imidazolines, the corresponding alkyl-substituted imidazo lidines, N~alkyl azepines, N-alkyl azocycloheptanes, iso azepine and A'-hexamethyleneimine, l-alkyl-, 5-alkyl- and 1,S-dialkyl-1,5-diazacyclooctanes, 1-alkyl-1,4-diazonines, N-alkyl azacyclooctaues, azocine, N-alkyl azocyclono nanes, 1-alkyl-, 4-alkyl- and 1,4-dialkyl-1,4-diazocyclodec anes, the various N-alkyl substituted 1,3-, 1,4- and 1,6 diazacyclohendecanes, and the various N-alkyl-substituted 1,2-, 1,4-, and 1,7-diazacyclododecanes, 2- and 4-isomida zoles, the various N-alkyl-substitution products thereof, the various N-alkyl pyrroles, pyrrolines and pyrrolidines, 2-pyrrolenine, 3-pyrrolenine, 1,3,5-dioxazine, l,'3,5,2-oxa diazine, 1,3,5,2-thiadiazine, 1,3,2-oxazine, l,3,4-'oxazine Also, there may be used the heteropoly forms of the acids of the acid 45 forming elements of group VI of the periodic table; Heteropoly acids of this kind which are suitable as catalysts in the process of this invention and methods for their prep are hereby incorporated into and made a part of the dis closures of this speci?cation. Of all of these catalysts, the 55 oxides, acids and acid salts of tungsten have proven to be the most useful due to their selectivity--i.e., their ability to promote the desired oxidation of the amine to the N ‘oxide with a minimum of undesirable side reactions—and to their high level of activity. Preferred catalysts therefore 60 are those which are based on tungsten, including tungstic oxide, tungstic acid, and the polytungstic acids, including both the homopolytungstic acids and the heteropolytung stic acids, and the salts of such acids, particularly the acid salts, including tungstic acid and the acid tungstates, boro 65 tungstic acid and borotungstates, chromotungstic acid and chromotungstates, phosphotungstic acid and phospho tungstates, selenotungstic acid and selenotungstates, and the like. . As a general rule, an amount of the catalyst between 70 about 1.0% and about 20%, based on the number of moles of amine reactant charged, will effectively catalyze the re and their thia analogs, pentoxazoline and N-alkyl pent oxazolidines, the N-alkyl ,homomorpholines, the various isomeric oxadiazepines, triazepines, oxazepines and their thia analogs, and the N-alkyl substitution products, N 75 action between the amine and the hydrogen peroxide. In many cases, even less of the catalyst-—e.g., as little as 0.1% of the amine on a molar basis-will be suf?cient, whilelin most cases it will be ‘found that ‘little additional 5 3,047,579 6 advantage over the use of lesser amounts of the catalyst are realized by using an amount of catalyst in excess of the case of the aliphatic tertiary amines. Suitable acids about 30% of the number of moles of amine charged. The hydrogen peroxide employed may be in the form of these, acetic acid and propionic acid are the most useful, an anhydrous gas, or liquid or it may be in the form of an aqueous solution containing from about 10% to about 90% by Weight of hydrogen peroxide. Particularly useful are the commercially available aqueous solutions con taining from about 35% to about 70% by weight of hy drogen peroxide. it is preferable that the highest prac tical concentration of hydrogen peroxide consistent with safe handlin? be employed because the presence or" higher concentrations of hydrogen peroxide in the reaction mix ture depresses the formation of side products and results in the formation of higher yields of the desired N-oxide product. For the same reason, ‘while it is quite feasible to employ stoichiometric quantities of the hydrogen per oxide relative to the amine reactant—-i.e., one mole of hydrogen peroxide per mole of amine~it is desirable that the hydrogen peroxide be present in the reaction Zone 20 in an amount somewhat in excess of the theoretical amount. The excess of hydrogen peroxide need not ex ceed about 100%, and in most cases an excess of hydrogen peroxide of about 50% will be found sufficient for the desired purpose. At least a 10% excess of hydrogen per oxide should be provided. The oxidation of the amine can be carried out at at mospheric, superatrnospheric or subatmospheric pressure, as may be desirable. In the great majority of cases, it will be found that operation at substantially atmospheric pressure will be found to be most convenient. Preferred temperatures for effecting the reaction are of the order of from about 40° C. to about 80° C, temperatures of from about 50 to 60° (3., being generally most useful. A temperature of at least about 25° C. will generally be found necessary to obtain practical reaction rates. In most cases, little advantage will be obtained through the use of temperatures in excess of about 100° C, as com pared to the use of somewhat lower temperatures. Under these conditions of temperature and pressure, reaction times of the order of from about one-half hour to about ten hours will be found suilicient to e?ect the desired reaction to completion. in many cases, the reaction of the amine and the hy drogen peroxide is most e?ectively carried out in a liquid phase reaction medium, using a solvent in which the hydrogen peroxide, and preferably also the catalyst, are substantially soluble. In ‘the case where the hydrogen peroxide is supplied as an aqueous solution, the solvent preferably also should be miscible with water. It is desir able that the solvent employed be substantialy inert with respect ‘to hydrogen peroxide under the conditions em ployed. Where the amine is an aliphatic amine in which are those containing up to about six carbon atoms. Of ' glacial acetic acid being preferred because of its wide availability at low cost. The amount of the solvent used is not critical. In gen eral, su?'lcient solvent should be employed to dissolve the intended solutes and to provide a readily ?uid reaction mixture. Generally a weight of solvent amounting to at least the weight of the amine reactant is required, and in most cases at least twice this amount of solvent is desirable. Usually, not more than about ?ve to ten times the weight of the amine reactant of solvent need be used. In most cases a weight of solvent of from about 3 to about 6 times the Weight of the amine reactant is most convenient. ‘It will be noted that as shown in Example ll, set out hereinafter, it is not always necessary, and in many cases is convenient and desirable, to conduct the reaction of the amine with the hydrogen peroxide without an added sol vent being present, since this avoids the cost of the sol vent and in many cases simpli?es recovery of the N-oxide product. In conducting the reaction of the amine and the hy drogen peroxide, it is desirable that the reactants be brought together slowly, and not all at once. The order in which the reactants are introduced into the reaction mixture is not critical. In most cases, it will be found most ‘desirable that the amine reactant be mixed with the catalyst (and solvent, if one is used) and the hydrogen peroxide added slowly to the stirred reaction mixture, the reaction temperature being controlled by heating or cool ing as necessary. This is not to say that the reverse order of mixing may not be used. However, addition of the hydrogen peroxide to the amine is the preferred technique, since it permits better control of the reaction and mini mization of undesired byproducts. It is desirable that the reaction mixture pH be main tained at 7 or less-that is, alkaline reaction mixtures are preferably avoided~since the hydrogen peroxide tends to decompose in alkaline solution without forming useful product. Preferably the reaction mixture is slightly to moderately acid. This acid condition is provided, of course, where a lower monocarboxylic acid is used as solvent. It also is attained where the catalyst is an acid, and especially where the acid used as catalyst is soluble in ‘the reaction mixture. In some cases, where there is encountered a tendency for decomposition of the hydrogen peroxide, the decom position of the hydrogen peroxide ‘can be reduced by the addition of ‘a small amount of a chelating agent, such as ethylene diaminetetraacetic acid or other aminopoly carboxylic acid, or salt thereof. the amino nitrogen atom is not a part of a heterocyclic In the great majority of cases, when the disclosed pro ring, such non~acidic solvents as the oxygenated organic 55 portions of hydrogen peroxide and amine are employed, liquids such as alcohols, hydroxy others, ketones and the the hydrogen peroxide will be consumed in the reaction like can be used effectively. While any of the alcohols can be used for the purpose, it is preferred to use the lower 'alkanols substantially miscible with water—for ex ample, the alkanols of up to ‘about ?ve carbon atoms. and/or any excess will be decomposed in the reaction mixture, so that no problem of removing unreacted hy drogen peroxide from the reaction mixture is presented. Tertiary butyl alcohol has been found particularly useful. Suitable hydroxy-ether solvents include, for example, the drogen peroxide is used, there may be excess hydrogen ethylene glycol and diethylene glycol monoethers, partic— ularly the ethyl ethers. Dioxolane, dimethyl formamide and sulfolane are other types of solvents which can be successfully used. Lower aliphatic ketones, however, have proven to be particularly effective. Of these the ketones of up to about six carbon atoms, and particularly In a few cases, however, as Where a large excess of hy peroxide present in the reaction mixture and it may not be convenient or desirable to continue the reaction until all of the excess hydrogen peroxide has been decomposed. In such cases, the excess hydrogen peroxide is decom posed by conventional methods, such as addition of platinum black or other hydrogen peroxide decomposition dimethyl ketone and methyl ethyl ketone, have been catalyst, and/or by addition of a strong base, such as found of marked usefulness. 70 sodium hydroxide, followed by heating as necessary to Where the amine reactant involves an aromatic group, decompose the excess hydrogen peroxide. The presence or is a beterocyclic amine in which the amine nitrogen or absence of hydrogen peroxide in the reaction mix atom is a part of the hetero ring, it has been found that ture can be ascertained by analyzing small portions of the most useful ‘solvents are the lower aliphatic mono carboxylic acids. the mixture by Kingzett’s iodide methodv (employing These acids also ‘are quite useful in 75 potassium iodide and sodium thiosulfate), Furman, 3,047,579 “Scott’s Standard Methods of Chemical Analyses,” 8th edition, 1939, at page 2180. The catalyst is removed from the ?nal reaction mixture by one or two general techniques, the particular technique used ‘being dependent upon whether or not the catalyst is soluble in the reaction mixture. If the catalyst is in soluble, it can be removed by ?ltration, centrifugation or similar technique-s. If the catalyst is soluble, it is best 8 heated to 60° C. and stirred vigorously. 8.2 parts of a solution of 50% by weight hydrogen peroxide in water was added to the stirred mixture over a period of ?ve minutes, the reaction temperature being held at about 60-65" C. The mixture was stirred and maintained at about 60—65° C. for an additional ?ve hours, when all of the peroxide had been consumed (as determined by titra tion of one milliliter samples of the reaction mixture using the potassium iodide-sodium t-hiosulfate rvolumetric tech removed by extraction of the reaction mixture with a suit able selective solvent, which in many cases‘may be a lower 10 nique). The mixture was ?ltered to remove the catalyst, a 10% excess over the stoichiometric amount of concen aliphatic ether, such as diethyl ether. The technique for removal of the catalyst may also depend upon the technique by which the N-oxide product is recovered. In trated hydrochloric acid wa added and the acetic acid and Water were removed by distillation of the mixture under any case, the catalyst normally can be reused without further treatment. In some cases, it will be found that parts of product were obtained. This was an 85% yield. the catalyst is insoluble, but that the particles thereof are of colloidal dimensions, so that removal of the catalyst by ?ltration or centrifugation is dif?cult. In such cases, Repetition of this experiment, substituting 10.1 parts of triethylamine for the pyridine results in approximately the same yield of triethylamine oxide. removal of the catalyst is more easily accomplished by treating the reaction mixture containing the catalyst with Example II a pressure of 15-20 millimeters mercury pressure. 11.2 an ‘alkaline earth metal base, such as calcium hydroxide 5 parts of tungstic acid and 22.7 parts of Z-chloro preferably in solution in water, the amount of the base pyridine were mixed and to the mixture was added drop being slightly in excess of the stoichiometric amount re wise over a 5-minute period 23.4 parts of a solution of quired to react with all of the'a-cidic catalyst. The mixture 35% by weight hydrogen peroxide in water. The mixture 25 is stirred for about 30~90 minutes, preferably while cool was stirred and heated to about 60—65° C. for six hours. ing from reaction temperature down to room temperature. Then 23 parts of concentrated hydrochloric acid were The base reacts with the acidic catalyst, the‘ resulting added, the mixture was heated on a steam bath for about salt being stable and easily coagulated and removed by ?ltration and/or centrifugation techniques. The catalyst 15 minutes, was allowed to cool and was ?ltered to re .move the catalyst. The ?ltrate was evaporated to dry is recovered ‘for re-use by springing the acid from the salt. 30 ness under 15~20 millimeters mercury pressure. 22.6 parts The N-oxide product can be recovered from the cata of the hydrochloride of 2-chloropyridine N-oxide, repre lyst-free mixture in a number of ways. In cases where senting a 78% yield based on the amine reactant, were anhydrous hydrogen peroxide was used, ‘and no solvent was used, or in cases where aqueous hydrogen peroxide was used, and no solvent was used, the product N-oxide 35 obtained. Example 111 may often be recovered by simply distilling oif the water of reaction and water introduced with the hydrogen perox 18.6 parts of gamma-picoline, 60 parts of tertiary butyl an alkaline aqueous medium. In those cases, the N-oxide was added over a ?ve minute period. The mixture was maintained at 60-65 ° C. with stirring for an additional 2.5 ‘alcohol, and 5.0 parts of tungstic acid were mixed and ide. Where a solvent was used, in many cases the solvent stirred vigorously at 60° C. 16.4 parts of 50% by weight too may be removed by distillation. It must be noted hydrogen peroxide in water was added over a ?ve-minute that in a great many cases the N-oxide product is some 40 period. The mixture was stirred and heated at 60-65° what unstable, so that distillation of the water or water C. for six hours. At that time all of the peroxide had and solvent must be accomplished at such a low pres sure that the N-oxide product is not decomposed. It has , been consumed. The mixture was ?ltered to remove the catalyst and the alcohol and water were removed by distil been found that in a great percentage of cases, the hydro lation of the solution under a pressure of 15-20 milli halide (e.g., hydrochloride) of the N -oxide is more stable meters mercury pressure. 14.7 parts of the product gam than is the N-oxide itself. In such cases, the N-oxide is ma-picoline N-oxide remained. This represented a 72.5% best recovered by ?rst converting it to the hydrohalide, yield. then removing water or water and solvent. Also, the N Example ‘I V oxide hydrohalides usually are crystalline, whereas the N oxides are not; conversion of the N-oxide to the hydro. 25.8 parts of quinoline, 60 parts tertiary butyl alcohol, halide thus provides a simple technique for obtaining a and 5.0 parts of tungstic acid were mixed and heated to pure product by recrystallization techniques. 60° C. 16.4 parts of 50% by weight hydrogen peroxide In some cases, the N-oxide is substantially insoluble in may be conveniently recovered by making the crude re action mixture freed of any solid catalyst alkaline (as by addition thereto of a strong base, such as sodium hydroxide) and separating the insoluble N-oxide from the resulting mixture. 00 The foregoing constitutes 1a general description of the process of this invention. The following examples are set out to demonstrate application of the process to the prep aration of particular N-oxides from particular amines. These examples are included in this speci?cation only for the purpose of illustrating and exemplifying the inven tion, and are not to be construed as limiting the invention in any way not recited in -the claims of this application. hours. The N-oxide was isolated as in the above example in a 70% yield (20.3 parts product as the N-oxide). Example V 31.6 parts of pyridine, 20 parts water, and 5.0 parts of molybdic anhydride were mixed together and heated to 60° C. 32.8 parts of 50% by Weight hydrogen peroxide was added over a ten minute period. The temperature of the reaction mixture was maintained at 60~65° C. for two hours until all of the peroxide was consumed. 4.0 parts of calcium hydroxide were added and the tempera ture of the reaction mixture was allowed to cool to room In these examples, “parts” means “parts by weight” unless temperature with continued stirring. The insoluble salts 70 otherwise speci?cally indicated. were ?ltered. Fifty parts of concentrated hydrochloric acid were added to the ?ltrate. The solution then was Example I freed of water by distillation at 10~15 millimeters mercury pressure. 34.3 parts of the hydrochloride salt of the pyri and 2.5 parts of tungstic acid were mixed and the mixture 75 dine N-oxide was obtained, representing a 63% yield. 7.9 parts of pyridine, 30 parts of glacial acetic acid 3,047,579 9 10 Iclaim as my invention: 1. A process for preparing N-oxides which comprises reacting: (a) a compound of the formula: alcoho1_ solvent with a catalytic amount of pertungstic acid. 6. A process of preparing the N-oxide of pyridine in a car‘ocxylate-free environment which comprises reacting: ' 5 (a) pyridine and (b) hydrogen peroxide at a tempera ture of from 40° C. to 80° C. in the presence of a catalytic amount of an inorganic per-compound of an acid-forming element selected from the group consisting of the elements of group VI of the periodic table. 10 7. The process of claim 6 in which the per-compound is a molybdenum compound. 8. A process for preparing the N-oxide of quinoline wherein all of the ring substituents except M are hydrogen which comprises reacting quinoline and hydrogen peroxide atoms and M is selected from the group consisting of hy in a carboxylate-free environment at a temperature of drogen, chlorine, and methyl, and (b) hydrogen peroxide at a temperature of from 40° C. to 80° C. in the presence 15 from 40° C. to 80° C. in the presence of an inorganic per compound of an acid-forming element selected from the of a catalytic amount of an inorganic per-compound of an group consisting of the elements of group VI of the acid-forming element selected from the group consisting periodic table. of the elements of group VI of the periodic table. 2. A process for preparing the N-oxide of 2-chloropyriRefmemes Citg? in the ?le of this patent dine which comprises reacting: 20 (a) 2-ch1oropyridine and (b) hydrogen peroxide at a UNITED STATES PATENTS temperature of from 40° C. to 80° C. in the presence of a catalytic amount of an inorganic per-compound of an acid-forming element selected from the group consisting of the elements of group VI of the periodic table. Van Aren-donk ______ __ Feb. 25, 1947 Evans et al. __________ __ Aug. 5, 1950 199,451 Switzerland ___________ __ Nov. 1, 1938 25 3. The process of claim 2 wherein the per-compound is a tungsten compound. 2,416,658 2,518,130 FOREIGN PATENTS ' T h 4. The process of claim 2 wherein the per-compound is OTi-IER REFERENCES ' atungstic acid compound. Baxter et al.: Chem. Abstracts, vol. 44, column 8356 5. A process for preparing the N-oxide of gamma-pico- 30 (1950). line in a carboxylateiree medium which comprises react.ierehel et al.: Chem. Ber., vol. 85, pages 1130-8 ing: (1952). (a) gamma-picoline and (b) hydrogen peroxide at a temperature of from 40° C. to 80° C. in tertiary butyl Culvencr: Chem. Abstracts, vol. 48, column 4432 (1954).